Web processing apparatus

ABSTRACT

A web tensioning assembly is configured to exert a tension on a web in a process direction and to balance the tension across a width of the web extending substantially in a direction perpendicular to the process direction. A web processing apparatus includes such a web tensioning assembly.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Application No. 60/960,952, filed on Oct. 22, 2007, theentirety of which is expressly incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a web tensioning assembly configured toexert a tension on a web in a process direction and to balance thetension across a width of the web extending substantially in a directionperpendicular to the process direction. The present invention alsopertains to a web processing apparatus comprising such a web tensioningassembly.

2. Description of Background Art

Web tensioning assemblies that exert a tension on a web in a processdirection are known in the background art. An example of such assemblyis a suspended roller assembly. Such assembly comprises a rollerrotatably mounted on an axis that is mounted on two linkages, which aremounted freely rotatable in a frame. If the web is fed in a curve aroundsuch a roller, the position and weight of the roller exerts a tension onthe web in the feed direction. Such arrangement call; however, notaccount for differences in path length across the width of the web,resulting in a variation in tension across the web.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a web tensioningassembly for applying tension in a process direction that takes intoaccount differences in path length across the width of the web. To thisend a web tensioning assembly according to an embodiment of presentinvention for tensionably guiding a web in a web processing apparatus,comprises an elongated torsion-resilient element extending in an axialdirection having at least two opposing axial end portions; a suspensionthat suspends said elongated torsion-resilient element, the suspensioncomprising a first and second suspension linkage, each linkage beingnon-rotatably connected to the opposing axial end portions of theelongated torsion-resilient element at a first portion of the first andsecond suspension linkages, respectively, the first and secondsuspension linkages being rotatably mountable to a frame at a secondportion of the first and second suspension linkages, the second portionbeing located remotely with respect to said first portion, such that thefirst and second suspension linkages are independently rotatable aboutan axis extending substantially parallel to said axial direction; and aweb guide at least partially surrounding the elongated torsion-resilientelement for guiding the web over said elongated torsion-resilientelement, wherein the web tensioning assembly is configured to exert atension on the web in a process direction and to balance the tensionacross a width of the web extending substantially in a directionperpendicular to the process direction.

The web tensioning assembly for tensionably guiding a web in a webprocessing apparatus according to the present invention, takes intoaccount applying a tension in a transport or processing direction whilethe web is transported along the web transport path. The web tensioningassembly comprises an elongated torsion-resilient element, which extendsin an axial direction. The elongated torsion-resilient element isresilient to a torsional loading of the element. If a torsional load isapplied on the elongated torsion-resilient element, e.g. an axialtorsional load, the elongated torsion-resilient element may deform to acertain extent while resisting against said deformation.

The elongated torsion-resilient element is suspended on the axial endportions of the elongated torsion-resilient element on a suspension. Thesuspension comprising a first and a second suspension linkage, which areboth non-rotatably connected to the opposing end portions of theelongated torsion-resilient element at a first portion of the first andsecond suspension linkages.

The first and second suspension linkages are rotatably mountable to aframe at a second portion of the suspension linkages. The second portionof the first and second suspension linkages are located remotely withrespect to the first portion, thereby constituting a mechanical armbetween the end portions of the elongated torsion-resilient element andthe points of rotation at the second portion on which the suspensionlinkages are rotatably mountable to the frame.

The first and second suspension linkages are independently rotatable atthe second portions of the first and second suspension linkages about anaxis extending substantially parallel to the axial direction of theelongated torsion-resilient element.

The web tensioning assembly farther comprises a web guide that guidesthe web over the elongated torsion-resilient element. This web guidesurrounds the elongated torsion-resilient element at least partially.

The web tensioning assembly is arranged such that the web tensioningassembly is configured to exert a tension on the web in the processdirection and balances the tension across the width of the web. Thewidth of the web is the width of the web in the direction extendingsubstantially perpendicular to the process direction.

By arranging the web tensioning assembly, e.g. such that the web guiderests on the web on a position where the web transport path is curved,the arrangement of the web tensioning assembly creates a force by meansof the weight of the web tensioning assembly, which is, via themechanical arm of the suspension linkages, transferred onto the web viathe web guide, thereby exerting a tension on the web in processdirection. If, during operation, a difference in path length occursacross the width of the web, the web tends to curve due to path lengthdifferences of the web. By the curving of the web across the width ofthe web, the web may exert a non-uniform mechanical pressure on the webguide. By exerting a non-uniform mechanical pressure on the web guide,the web guide may be rotated to some extent about an axis of rotationextending parallel to the process direction. The web guide passes thisrotation on to the elongated torsion-resilient element, following therotation of the web guide. Because the elongated torsion-resilientelement is non-rotatably connected to the suspension linkages, which areindependently rotatable, the rotation of the web guide is transferredinto a torsional deformation of the elongated torsion-resilient element.This elongated torsion-resilient element deforms to a certain extentwhile resisting against said deformation. This resisting against thedeformation urges the web guide back to the equilibrium position therebyurging the web into its normal orientation, correcting for path lengthdifferences across the width of the web.

It is further known to correct for path length differences across a web,by using a separate gimbal assembly. Such a gimbal assembly forces a webback into its normal transport path by introducing a rotational degreeof freedom in the web transport path, which is resiliently urged towardsa desired equilibrium situation.

It is a disadvantage of such a gimbal assembly, that such a gimbalassembly introduces an additional degree of freedom in at least aportion of the web transport path, thereby introducing a position ofuncertainty. Such a position of uncertainty in the web transport pathdegrades the accuracy of the web transport and introduces complexity indriving the transport means of the web transport path by means ofservomotors.

Using the gimbal assembly in sequential addition to a web tensioningassembly increases the required cumulative space of these assemblies, inparticular because the separate application of a gimbal assembly insequential addition to a web tensioning assembly needs a stretch of webbetween both assemblies to be able to introduce the necessary degree offreedom of the web at the gimbal assembly.

The functional merging of the web tensioning function in the processdirection and the balancing of the tension across the width of the webincreases the quality of the web transport in the web transport path.While the application of the separate functions requires a stretch ofweb in between the two functions, in the present invention, bothfunctions are merged into one location. This reduces the required spaceto house both functions, and reduces the stretch of the web inbetweenthe web tensioning in the process direction and the balancing of thetension across the width of the web. A large tension across the width ofthe web may result in damaging the web and even tearing of the web,thereby rendering the web possibly unusable.

In an embodiment of the web tensioning assembly according to the presentinvention, the web guide comprises a roller. Preferably, the rollersurrounds the elongated torsion-resilient element at least partially,such that the web guide guides the web via the roller over the elongatedtorsion-resilient element. A roller is advantageous because thisimplementation for the web guide enables a simple and efficient guidanceof the web, while deformations of the web due to tensional differencesacross the width of the web are easily passed towards the elongatedtorsion-resilient element.

In a further embodiment, the web tensioning assembly further comprises abearing for moveably mounting the roller on the elongatedtorsion-resilient element. A bearing such as, e.g. a ball bearing,dry-running, hydrodynamic or hydrostatic bearing, enables a smoothrotation of the web guide, in particular the roller over the elongatedtorsion-resilient element. Thereby the web guide minimizes the influenceon the motion of the transport of the web, while the web tensioningassembly applies its tension in the process direction.

In another embodiment, the roller of the web tensioning assembly isfreely rotatable about an axis of rotation extending substantiallyparallel to the axial direction of the elongated torsion-resilientelement. By enabling the roller to rotate freely about an axis ofrotation extending substantially parallel to the axial direction of theelongated torsion-resilient element, the roller's rotation influencesthe movement of the web transport minimally, while the deformation ofthe web due to tensional differences across the width of the web areeasily transferred into a resilient deformation of the elongatedtorsion-resilient element.

In another embodiment, the roller of the web tensioning assembly isrotatable over a limited portion of an axial revolution. The interfacingbetween the web and the web guide may be rolling or sliding, or anycombination of these interfacing types. By allowing a partial rotationof the roller, the web tensioning assembly is prevented to apply a toolarge frictional shear tension on the web.

In another embodiment, the roller of the web tensioning assembly isrotatably fixed in an axial direction with respect to the suspension,thereby creating a sliding interface between the web guide and the web.The web slides along the contacting surface of the web while the web isbeing transported in the process direction. In case of sliding,interfacing between the web and the web guide, the contacting surface ofthe web guide, which contacts the web during the transport of the web inthe process direction, is preferably smooth and applies a low frictionalforce in the process direction.

In a farther embodiment, the web tensioning assembly comprises a draglinkage extending between the frame and an eccentric location at anaxial end portion of the roller, such that an axial rotation of theroller is prevented. By mounting an element, such as a drag linkage,between the frame on which the web tensioning assembly is mounted and alocation of the roller, which lays at a distance with respect to theaxis of axial rotation of the roller, the axial rotation of the rolleris thereby prevented. It is found that locating the drag linkage at anend portion of the roller, e.g. the sides of the roller, near the outersurface of the roller, the drag linkage is most efficient, as thisapplies the largest mechanical arm to prevent a rotation of the roller.

In a further embodiment, the drag linkage is selectably engaged anddisengaged with the roller, thereby selectably enabling a sliding or arotating interfacing between the web guide and the web, respectively.The selection may, e.g. be implemented as a clamping of the drag linkageto the roller. When the drag linkage is clamped to the roller, theroller is prevented from rotating over the elongated torsion-resilientelement, and when the drag linkage is unclamped from the roller, theroller is freely rotatable with respect to the elongatedtorsion-resilient element.

In another embodiment, the suspension is in operation urged towards apredetermined angular equilibrium position with respect to the frame. Byapplying an urging force from the frame on the suspension, thesuspension will be urged towards an angular equilibrium position withrespect to the frame. This is, e.g. advantageous in cases where the webtensioning assembly does not apply its tensioning of the web in processdirection at a location along the web transport path where the web guiderests its full weight via the mechanical arm of the suspension on theweb. The urging of the suspension, in general enables an operator tochoose the tension that is applied on the web in the process directionand enables the web tensioning assembly to maintain a predeterminedequilibrium position, different from the fully resting position, i.e.the situation in which the suspension is freely rotatable with respectto the frame and no urging force is applied from the frame to thesuspension. The urging force from the frame to the suspension ispreferably applied on both suspension linkages, but may also be appliedto only one of the suspension linkage.

In a further embodiment, the suspension is spring loaded towards thepredetermined angular equilibrium position. A spring enables theconfiguration of the equilibrium position to be carried out with asimple construction. Depending on the actual arrangement of the springwith respect to the suspension, the web guide is supported by the springor alternatively an additional pressure is applied on the web via theweb guide, e.g. may be implemented by directing the spring force in thedirection of the gravitational movement of the web guide.

In another embodiment of the web tensioning assembly according to thepresent invention, the elongated torsion-resilient element is a torsionbar. The torsion bar is an element, which resiliently deforms under atorsional load. The relation between the deformation of the torsion barand the torsional load may be chosen to fulfil the desired behavior ofthe elongated torsion-resilient element. Torsion bars may be designed toperform a deformation in linear proportional relation with the appliedtorsional load, or may be chosen to have a non-linear relation with theapplied torsional load. A linear relation will be appreciated inparticular when the deformation, and the proportional resisting counterforce or the elongated torsion-resilient element, should increase in alinear fashion when the torsional load on the elongatedtorsion-resilient element increases. A non-linear relation will be inparticular appreciated when, e.g. the resisting counter force shouldonly come into play when the deformation of the elongatedtorsion-resilient element passes a certain threshold. The elongatedtorsion-resilient element may consist of a single torsion bar, or maycomprise a plurality of interconnected torsion-resilient sub-elements.

In a further embodiment, the torsion bar is formed such that itcomprises a substantially star shaped axial cross-section. A star shapedaxial cross-section of a torsion bar is in particular advantageous inconfigurations where the torsional load is applied in an axialdirection. Such a torsion bar may be formed as a single integral part,or be constructed, e.g. by joining two or more elongated strips ofmetal, plastics or the like.

In another further embodiment, the torsion bar is formed such that itcomprises a substantially cylindrical axial cross-section. A cylindricalformed axial cross-section of a torsion bar is in particularadvantageous in configurations where the torsional load is applied in anaxial and/or in process direction. Cylindrical torsion bars have ingeneral a very simple construction and may be relatively cheap.

In another embodiment, the suspension is functionally connected to anangular position encoder, such that the angular position of thesuspension with respect to the frame is measurable. By monitoring theangular position of the suspension linkages, the behavior of the webguide can be monitored. If the behavior occurs to be extraordinary, thismay point out that something should be adapted in the processing of theweb. Alternatively, this may be used to detect an absence of a web underthe web guide, in particular in configurations where the web guide restson the web, an absence of such a web is easily detectable using anangular position sensor measuring the position of the suspensionlinkages. Such a sensor may be implemented on one of the suspensionlinkages or on a plurality thereof.

In another aspect, the present invention pertains to a web processingapparatus, comprising a web feed station for feeding a web, a webprocessing station for processing the web and a web tensioning assemblyaccording to the present invention.

In a further embodiment of this aspect of the invention, the webprocessing apparatus comprises a printing station for applying markingmaterial to the web. It is important in such stations to provide the webin a defined fashion and therefore the web should be delivered under acertain tension in process direction, while the differences in pathlength and tension across the width of the web should be balanced toperform a printing operation on defined positions of the web.

In a further embodiment of this aspect of the invention, the webprocessing apparatus comprises a recording station for recording animage from the web. It is important in such stations to provide the webin a defined fashion and therefore the web should be delivered under acertain tension in process direction, while the differences in pathlength and tension across the width of the web should be balanced toperform a recording operation on defined positions of the web.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a perspective view of an embodiment of a printing device;

FIG. 2A is a first perspective view of an embodiment of a roll-to-rollweb processing device according to the present invention for use withthe printing device of FIG. 1;

FIG. 2B is a second perspective view of the embodiment of theroll-to-roll web processing device of FIG. 2A;

FIG. 3A is a first schematic perspective view of an embodiment of theweb tensioning assembly of the roll-to-roll web processing device ofFIGS. 2A and 2B;

FIG. 3B is a second schematic perspective view of an embodiment of theweb tensioning assembly of the roll-to-roll web processing device ofFIGS. 2A and 2B;

FIG. 4A is a schematic illustration of the nominal configuration of theweb tensioning assembly;

FIG. 4B is a schematic illustration of a deformed configuration of theweb tensioning assembly;

FIG. 5A is a schematic front view of the nominal configuration of theweb tensioning assembly;

FIG. 5B is a schematic front view of a first deformed configuration ofthe web tensioning assembly; and

FIG. 5C is a schematic front view of a second deformed configuration ofthe web tensioning assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described with reference to theaccompanying drawings, wherein the same reference numerals have beenused to identify the same or similar elements throughout the severalviews.

FIG. 1 illustrates a printing device 10 for printing an image or text ona relatively large object, in particular on a relatively large and flatobject. Such a printing device 10 is well known in the background art.The printing device 10 includes a support assembly 12 on which aprinting surface 14 is arranged. As illustrated, the printing surface 14may be provided with suction holes for pulling the object onto theprinting surface 14 and thereby holding the object flat on the printingsurface 14. A guiding assembly 16 is provided for supporting and guidinga carriage 18. The carriage 18 is movably supported by the guidingassembly 16 such that the carriage 18 may be moved over the printingsurface 14. For example, the guiding assembly 16 may be movablysupported on the support assembly 12 such that the guiding assembly maybe moved in a y-direction (as indicated in FIG. 1) and the carriage 18may be moveably supported by the guiding assembly 16 such that thecarriage may be moved in a x-direction guided by the guiding assembly16. The carriage 18 is provided with a printing element such as aninkjet printhead for printing the image or the text on the objectarranged on the printing surface 14 by ejecting ink drops atpredetermined positions. It is noted that the guiding assembly 16 and/orthe carriage 18 may be supported such that they may be moved in az-direction, thereby enabling printing on different media (i.e. objects)having a different dimension in the z-direction (when positioned on theprinting surface 14).

The printing device 10 further includes an interface assembly 20. Theinterface assembly 20 is configured for connecting a roll-to-roll webprocessing device to the printing device 10 such that the printingdevice 10 is enabled to print on a media that is supplied from a rollinstead of a medium that is positioned on the printing surface 14,although it is noted that in an embodiment the medium that is suppliedfrom a roll may be moveably supported by, guided over and positioned onthe printing surface 14. In such an embodiment, the medium may betransported from a supply roll arranged at a first side of the printingsurface 14 to a media receiving roll arranged at a second side of theprinting surface 14. Hereinafter, an embodiment, which is illustrated inthe drawings, is elucidated, in which embodiment a media supply roll anda media receiving roll are arranged at one side of the printing surface14.

FIGS. 2A and 2B illustrate a roll-to-roll web processing device 22configured to be coupled to the printing device 10 of FIG. 1. Theroll-to-roll web processing device 22 includes a first media roll slot24 and a second media roll slot 26 for supporting two media rolls. Inparticular, in the illustrated embodiment, a first media roll may supplya medium, while a second media roll may receive the medium after it hasbeen printed. For supporting the media rolls, each slot 24, 26 isconfigured for receiving a media roll supporting device 28. The mediaroll supporting device 28 is configured to receive and support the mediaroll. The media roll supporting device 28 includes an elongated elementaround which the media roll may be arranged. The elongated element maybe a bar or axle having a cylindrical cross-section, for example. Alsoother suitable shapes may be employed. The media roll supporting device28 further includes a support and may further include an assembly of anumber of parts, possibly providing additional functionality. In anycase, the media roll supporting device 28 is removeably supported in atleast one slot 24, 26; preferably the media roll supporting device 28 issupported in a suitable slot 24, 26 at each end of the media rollsupporting device 28.

For printing, the medium supplied from a roll arranged in theroll-to-roll web processing device 22 is guided through the roll-to-rollweb processing device 22 such that the media is moveably supported byand positioned on a media printing surface 30, possibly provided with adevice that holds the medium substantially flat on the media printingsurface 30. Such holding device may include, but is not limited to, asuction device. For guiding, one or more medium guiding rolls may beprovided. For example, a first guiding roll 32A and a second guidingroll 32B may be provided. The second guiding roll 32B, in combinationwith mechanisms 40A and 40B form a web tensioning assembly according tothe present invention.

One or both media rolls may be driven by a motor 36, for example throughthe media roll supporting device 28 supporting the media roll. In FIGS.2A-2B, the motor 36 is arranged at one side of the roll-to-roll webprocessing device 22. Hence, each media roll supporting device 28 isdriven at one end thereof. In an embodiment, a motor 36 may be providedat both ends of the media roll supporting device 28. As shown in FIG.2B, a drive coupling 38 is provided for operatively coupling the motor36 and the media roll supporting device 28.

FIGS. 3A and FIG. 3B are schematic perspective views of an embodiment ofthe web tensioning assembly 50 of the roll-to-roll web processing deviceof FIGS. 2A and 2B. Mechanisms 40A and 40B are mounted on a respectiveportion of the frame 45A and 45B. Mechanisms 40A and 40B respectivelyinclude suspension linkages 49A and 49B, which are non-rotatablyconnected to torsion bar 55 at a first portion of the respectivesuspension linkages 49A and 49B. The respective suspension linkages 49Aand 49B are rotatably mounted to the portions of the frame 45A and 45Bat a second portion of the respective suspension linkages 49A and 49B,thereby forming a mechanical arm between the point of rotation at thesecond portions and the first portions on which the torsion bar 55 arenon-rotatably connected. The torsion bar 55 is connected to thesuspension linkages 49A and 49B by means of respective collars 54A and54B, which are fixedly clamped on the torsion bar 55 and are connectedto the suspension linkages 49A and 49B by means of two bolts each.

Flanges 59A and 59B are rotatably mounted over the torsion bar 55, aswell as roller carrier flanges 58A and 58B. The flanges 58A, 58B, 59Aand 59B are mounted on the torsion bar 55 by means of a dry-runningplastic bearing bushing 52. Flange 59A and roller carrier flange 58A arenon-rotatably connected to each other by means of bolts, just as theopposing pair of flanges.

Suspension linkage 49A is connected to an angular position sensor 56,which measures the angular orientation of the suspension linkage 49A.The signal of the sensor 56 is fed to a signal processing unit (notshown).

The rotation of the coupled flanges 59B and 59A is prevented by draglinkage 51, which is connected to the frame 45B and a portion of theflange 59B remote from the axis of rotation.

FIG. 3B illustrates the situation in which a roller 60 is fitted on theconstruction as presented in FIG. 3A. The roller 60 is mounted on theroller carrier flanges 58A and 58B by means of a wringing fit. Incombination with the drag linkage 51, the roller 60 is prevented fromrolling along with the web, creating a sliding interface between theroller 60 and the web.

As depicted in FIGS. 2A and 2B the web transport path curves up at theweb tensioning assembly 50. The weight of the web tensioning assemblyrests in the curve of the web. Suspension linkage 49B is provided with aspring loading assembly 53 to controllably influence the amount oftension that the web tensioning assembly exerts on the web. By means ofthis spring loading assembly 53 it is possible to urge the webtensioning assembly into a predetermined equilibrium position and/or toselectably control the amount of tension on the web.

FIG. 4A is a schematic illustration of the nominal configuration of theweb tensioning assembly and FIG. 4B is a schematic illustration of adeformed configuration of the web tensioning assembly. The webtensioning assembly is equipped with a star shaped torsion bar 55. Forreasons of clarity the web guide, in particular the roller is not shown.

In the situation of FIG. 4A, the web slides or rolls along the web guide(not shown) and is kept at the required tension in the processdirection, i.e. the transport direction.

In the situation of FIG. 4B, the web is transported along the web guide,but a path length difference occurs. Therefore, in the depictedsituation, the web tends to curve such that the side of the web nearlinkage 49B is pushed slightly downwards and the portion near linkage49A is pulled up slightly. The web guide rotates accordingly and urgesthe torsion bar 55 accordingly as depicted. Because the torsion bar 55is non-rotatably connected to both suspension linkages 49A and 49B, thetorsion bar 55 is twisted over its length. This twisting deformationinvokes a counter-force generated by the torsion bar 55, which urges thetorsion bar back into the situation of FIG. 4A. By returning into thesituation of FIG. 4A, the torsion bar 55 pushes the web guide along. Theweb guide, in this case the roller (not shown), pushes the web back intoits nominal equilibrium position.

FIG. 5A is a schematic front view of the nominal configuration of theweb tensioning assembly, FIG. 5B is a schematic front view of a firstdeformed configuration of the web tensioning assembly and FIG. 5C is aschematic front view of a second deformed configuration of the webtensioning assembly.

FIGS. 5A, 5B and 5C illustrate another effect that exerts the torsionbar 55 when the web guide is tilted by the web due to path length andtension differences across the width of the web. Because the torsion bar55 is non-rotatably connected to the suspension linkages 49A and 49B,also non-rotatable in a direction of rotation perpendicular to the planeof the figure, a relative movement of the suspension linkages result ina torsional load on the torsion bar 55, urging the torsion bar 55 intoan S-shaped deformation over its length as depicted in FIG. 5B and FIG.5C.

FIG. 5A illustrates the nominal equilibrium position of the webtensioning assembly, comparable to the situation as depicted in FIG. 4A.The torsion bar 55 is partly surrounded by a web guide, here a roller60, which is freely rotatably mounted on torsion bar 55 by means of adry-running bearing bushing 52A and 52B.

FIGS. 5B and 5C depict the deformed situations where the nominalsituation of the suspension of FIG. 5A is depicted in dashed lines. Thetorsion bar 55 is deformed in an S-shape as the resilient character ofthe torsion bar 55 urges the torsion bar 55 back into its nominalstraight shape, urging the roller 60 along with it. Therefore, thiseffect also contributes to the balancing of the tension differencesacross the width of the web.

In practice, it shall be clear that both the effects of FIGS. 4A and 4Band the effect of FIGS. 5A, 5B and 5C may occur at the same time anddepending on the actual resilient properties of the torsion bar 55; anyone of the effects may prevail over the other ones.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A web tensioning assembly for tensionably guiding a web in a webprocessing apparatus, comprising: an elongated torsion-resilient elementextending in an axial direction having at least two opposing axial endportions; a suspension that suspends said elongated torsion-resilientelement, the suspension comprising a first and second suspensionlinkage, each linkage being non-rotatably connected to the opposingaxial end portions of the elongated torsion-resilient element at a firstportion of the first and second suspension linkages, respectively, thefirst and second suspension linkages being rotatably mountable to aframe at a second portion of the first and second suspension linkages,the second portion being located remotely with respect to said firstportion, such that the first and second suspension linkages areindependently rotatable about an axis extending substantially parallelto said axial direction; and a web guide at least partially surroundingthe elongated torsion-resilient element for guiding the web over saidelongated torsion-resilient element, wherein the web tensioning assemblyis configured to exert a tension on the web in a process direction andto balance the tension across a width of the web extending substantiallyin a direction perpendicular to the process direction.
 2. The webtensioning assembly according to claim 1, wherein the web guidecomprises a roller.
 3. The web tensioning assembly according to claim 2,further comprising a bearing for moveably mounting the roller on theelongated torsion-resilient element.
 4. The web tensioning assemblyaccording to claim 2, wherein the roller is freely rotatable about anaxis of rotation extending substantially parallel to the axial directionof the elongated torsion-resilient element.
 5. The web tensioningassembly according to claim 2, wherein the roller is rotatable over alimited portion of an axial revolution.
 6. The web tensioning assemblyaccording to claim 2, wherein the roller is rotatably fixed in the axialdirection with respect to the suspension.
 7. The web tensioning assemblyaccording to claim 6, further comprising a drag linkage extendingbetween the frame and an eccentric location at an axial end portion ofthe roller, such that an axial rotation of the roller is prevented. 8.The web tensioning assembly according to claim 1, wherein the suspensionis in operation urged towards a predetermined angular equilibriumposition with respect to the frame.
 9. The web tensioning assemblyaccording to claim 8, wherein the suspension is spring loaded towardsthe predetermined angular equilibrium position.
 10. The web tensioningassembly according to claim 1, wherein the elongated torsion-resilientelement is a torsion bar.
 11. The web tensioning assembly according toclaim 10, wherein the torsion bar is formed such that it has asubstantially star-shaped axial cross-section.
 12. The web tensioningassembly according to claim 11, wherein the torsion bar is formed suchthat it has a substantially cylindrical axial cross-section.
 13. The webtensioning assembly according to claim 1, wherein the suspension isfunctionally connected to an angular position encoder, such that theangular position of the suspension with respect to the frame ismeasurable.
 14. A web processing apparatus, comprising: a web feedstation for feeding a web; a web processing station for processing theweb; and a web tensioning assembly for tensionably guiding the web, saidweb tensioning assembly comprising: an elongated torsion-resilientelement extending in an axial direction having at least two opposingaxial end portions; a suspension that suspends said elongatedtorsion-resilient element, the suspension comprising a first and secondsuspension linkage, each linkage being non-rotatably connected to theopposing axial end portions of the elongated torsion-resilient elementat a first portion of the first and second suspension linkages,respectively, the first and second suspension linkages being rotatablymountable to a frame at a second portion of the first and secondsuspension linkages, the second portion being located remotely withrespect to said first portion, such that the first and second suspensionlinkages are independently rotatable about an axis extendingsubstantially parallel to said axial direction; and a web guide at leastpartially surrounding the elongated torsion-resilient element forguiding the web over said elongated torsion-resilient element, whereinthe web tensioning assembly is configured to exert a tension on the webin a process direction and to balance the tension across a width of theweb extending substantially in a direction perpendicular to the processdirection.
 15. The web processing apparatus according to claim 14,wherein the web processing station comprises a printing station forapplying marking material to the web.
 16. The web processing apparatusaccording to claim 14, wherein the web processing station comprises arecording station for recording an image from the web.